A few years back I had a hobby (unrelated to CDing) that my wife didn't want to know about, and I wanted the freedom to pursue without explaining myself. So I opened a personal checking account that had a debit card connected to it. When I got some money it would be deposited in that account, then I could shop online without the SO being involved. She knew I was spending money, but didn't know what it was for.
It was a workable solution. The hardest part was getting the discretionary cash to deposit.
Good Luck.
